Figure Rotation and the Mass of the Galactic Bulge

Abstract

The mass of the Galactic bulge, $M_B$, is estimated from the tensor virial theorem. By including the effects of a barred stellar distribution and figure rotation (81 \kms kpc ${}^{-1}$) and by assuming that the bar is oriented at $\theta$ $=$ 20°\ to our line of sight, $M_B$ is found to be as high as 2.8$\times$10${}^{10}$ M${}_{\odot }$. This estimate is in good agreement with the total mass inferred from the observed optical depth to microlensing for stars toward the inner Galaxy. For larger angles, $\theta$ $\sim$ 40°, or smaller pattern speeds (20 \kms kpc ${}^{-1}$), $M_B$ is found to be $\sim$ 1.7 $-$ 1.9$\times$10${}^{10}$ M${}_{\odot }$, similar to previous estimates for a barred bulge (2$\times$10${}^{10}$ M${}_{\odot }$) and axisymmetric bulge (1.8$\times$10${}^{10}$ M${}_{\odot }$).

10 pages, no figures, uuencoded postscript. Accepted for publication in the Astrophysical Journal Letters.

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